A ball valve is a kind of ball valves using a ball as the on-off member; the valve is fully open when turned to where the central through bore of the ball is coaxial with the valve passage, and fully closed when perpendicular to the valve passage. The prior art has had two types of ball valves, one floating ball valve and one trunnion-mounted ball valve. The invention, besides improving the designs of the two types of ball valves, proposes a seat-mounted ball valve. As we know, the floating ball valve is a kind of ball valves whose on-off ball is to float and whose seats is generally mounted under medium pressure for realizing the tight closure, whereas the trunnion-mounted ball valve is a kind of ball valves whose on-off ball is mounted in valve body by trunnions or whose seat is to float under medium pressure for realizing the tight closure. Therefore, the seat-mounted ball valve of the invention is a kind of ball valves whose on-off ball is mounted in valve body by valve seats, or neither whose seat nor whose ball is to float under medium pressure for realizing the tight closure.
The task of ball valve seats is to provide the oblique interface and seal between the on-off ball and the valve body. Therefore, a ball valve seat has at least three surfaces at an angle to each other: a ball-sealing surface, a body-sealing surface and a body-supported surface for force equilibrium. If designed only with the three surfaces, the ball valve seat would be enclosed for compression or have no exposure when the valve is fully closed or opened, or be of a triangular section.
The ball valve seat with an equilateral triangle as its section, having an equal acting force and an unequal bearing area for its each surface (due to a different forming radius), just satisfies the needs of unequal stresses for its each surface; the high stress on its ball-sealing surface is just its need for dynamic sealing, the intermediate stress on its body-sealing surface just its need for static sealing, and the low stress on its supported surface just its need for sliding on its supporting surface. Furthermore, the seat only with an equilateral triangle as its section can avoid a sharp corner weaker than 60°. Therefore, if of a triangular section, ball valve seats should be of an equilateral triangle section.
A polymer, such as PTFE, is the commonest valve seat material and typically has viscoelasticity, or has both viscous behavior of dense liquid (its strain lagging behind its stress) and elasticity of stable solid (its strain proportional to its stress). The viscous behavior of the seat material under unenclosed compression surely causes the material to creep (causing a sealing stress relaxation) or to gradually deform and flow into extrusion gaps (causing a seal failure). Therefore, if the seat material is regarded as a most viscous liquid, the seat under enclosed compression is like the hydraulic oil in cylinders with no compressive deformation, no extrusive deformation or rupture and nowhere to creep as long as the extrusion gap is enough small, and has an actual bearing strength far higher than its material allowable strength.
Generally speaking, polymers used for valve seats, such as PTFE, have more than ten times the coefficient of thermal expansion of steel. Therefore, the more the mass or the greater the size of the material used for a valve seat, the more the thermal deformation of the seat relative to the valve body and the more likely to cause a seal failure. In other words, using an equilateral triangle section of ball valve seats can minimize their mass or size and further the thermal influence on their sealing reliability.
Heretofore, however, there have been no consideration of either using a ball valve seat of equilateral triangle sections or designing a ball valve seat or giving its dimensions by an equilateral triangle, and no further consideration of enclosing a ball valve seat for work as fully as possible.
A common ball valve seat has two exposures to the conveyed medium; one is exposed to and directly compressed by the medium in the flow passage, and the other, exposed to and directly compressed by the medium in the valve body cavity between the on-off ball and the valve body.
In order to prevent the upstream seat from being extruded or trapped into the central through hole of the on-off ball by the medium pressure on the seat exposure in the passage at the moment the valve is closing or opening, U.S. Pat. No. 6,948,699 designed a valve seat that is constrained in its mounting hole by a small inward circumferential step at the seat-mounting hole edge or by an O-ring between the seat and its mounting hole wall.
In order to reduce the extrusive flow and deformation of valve seat materials at the seat exposure in the cavity, a stop ring was increased on the exposure in U.S. Pat. No. 3,721,425, U.S. Pat. No. 4,410,165 and U.S. Pat. No. 6,969,047.
U.S. Pat. No. 293,057 and U.S. Pat. No. 4,385,747 prove that the prior art has often provided some axial vent grooves on the periphery of the seat ring to vent the fluid on the seat end face into the valve body cavity and to prevent the load on the upstream seat from being added on the ball and increasing the downstream seat load and the valve operation torque; however, at the moment the valve is fully opening, the horizontal portion of the seat will just face the ball bore and lose the spherical support of the ball, and the seat may be locally extruded into the ball bore and damaged if there is a flow through the seat end and the vent grooves; for this reason, the prior art can not help increasing the valve seat strength by enlarging its size or outside diameter or thickness and cause the valve seat to be more exposed.
In a word, the prior art has not known that the exposures of a ball valve seat have an influence on the free floating of its on-off ball, but has always thought that the ball of a floating ball valve will unconditionally float onto the downstream seat and enhance the tight closure thereon as the medium pressure increases.
As to the floating ball valve, as shown in FIG. 5, As represents the actuating area of medium on the ball, the circular area determined by the diameter Ds; p, the medium pressure; Ws=Asp, the ball floating force from medium (the thrust of medium on the ball); and W2, the ball clamping force from the seat. It is imaginable that the action force between the ball and the downstream seat is W2 when Ws≦W2 (at the time Ws is only to partially or just fully replace W2 at most but not added to the downstream seat), and is Ws but not W2 when Ws>W2 (at the time W2 has been fully replaced by Ws); i.e. as to the floating ball valve, the sealing force between the ball and the seat is either W2 or Ws or to realize the tight closure of a floating ball valve is to rely either on the ball clamping force W2 from the seat or on the ball floating force Ws from medium but never on both at the same time. Nevertheless, whichever to rely on shall be m times the unsealing force of medium on the seat (the thrust of medium on the seat) according to the concept of Appendix 2, Division 1, Volume VIII, ASME Boiler and Pressure Vessel Code; i.e. it is when W2 or Ws equals m(Ae+Ac)p that a floating ball valve can realize its reliable tight closure, where Ae is the seat's annular area exposed in the cavity, Ac the seat's annular area covered by the ball, Ae+Ac=Au the annular actuating area of medium on the seat to cause unsealing, p the pressure and m (the sealing maintaining factor)=the sealing actuation force/the unsealing actuation force. In other words, it is conditional for a floating ball valve to realize its tight closure by floating of its ball.
Supposing the closing seal of floating ball valves to be a self-energized seal, according to the concept of self-energized seals in Appendix 2, Division 1, Volume VIII, ASME Boiler and Pressure Vessel Code, the sealing maintaining factor m required of their seat is:m=[(W2−H)/Acp]≧0,or in mechanics the required of their seat is W2≧H=Aep (see FIG. 5),
where                W2=ball clamping forces from seats,        H=actuation forces Aep of medium on seat's annular exposures in cavity,        Acp=actuation forces of medium on seat's annular areas covered by balls,        Ae=seat's annular areas exposed in cavity,        Ac=seat's annular areas covered by balls, including non-contact areas Aep,        p=medium pressure.In other words, a floating ball valve will always maintain its tight closure by the ball floating force from medium as long as W2 (ball clamping forces from seats) is not less than Aep (actuation forces of medium on seat's annular exposures in cavity).        
In fact, a floating ball valve can not always maintain its tight closure by the ball floating force when W2≧Aep). For example, as shown in FIG. 5, when Ws (thrust of medium on balls)=W2 (ball clamping forces from seats), there must be W2(=Ws=Asp)>>Aep because As (actuating areas of medium on balls)>>Ae (seat's annular areas exposed in cavity), which has fully satisfied the above mentioned condition that W2(=Asp) is not less than Aep; but at the time, the ball just fully away from the upstream seat (because Ws is supposed to equal W2) will also lose the sealing contact with its downstream seat when in an eccentric drive inevitable and insurmountable: as soon as the acting Ws of the ball on the downstream seat is counteracted to a certain extent by the disturbing force resulted from the eccentric drive, the ball will get away from the intimate contact with its downstream seat and cause the pressurized medium more and more to permeate into the downstream seat areas covered by the ball so as to finally output a disturbing force Acp pushing the ball fully off its downstream seat; the greater the force Aep exerted on the seat exposure in the cavity, the more difficult the reviving of the ball clamping force W2 from the seat, which has been replaced by Ws, and the more beneficial to that the disturbing force Acp separates the ball from the downstream seat instantaneously; the ball, once away from the intimate contact with its two seats at the same time, will have medium actuation forces cancelling out each other and only float between its two seats or never recover the intimate contact with its two seats, however high the medium pressure p is; even the higher the medium pressure p, the larger the thrust (Ae+Ac)p of medium between and against the two seats and the more beneficial to that the ball has a more sufficient floating room between the two seats. In other words, it is impractical to consider the tight closure of floating ball valves per self-sealing or to ensure that their W2 (ball clamping forces from seats) is not less than their Aep (actuation forces of medium on seat exposures in cavity), for such a consideration can not eliminate the inherent ball-wedged disturbance from eccentric drive and not ensure the reliability of the tight closure.
From the above analysis, it can be seen that the seat's annular area Ae exposed in the cavity and the seat's annular area Ac covered by the ball are definitely related to an amplified output of the ball-wedged disturbance from eccentric drive, but the disturbing actuation force Acp of medium on the seat's annular area Ac has been definitely excluded in concepts and formulas when considering the closing seal of floating ball valves according to a self-energized seal. Therefore, such a consideration can not relate at all the resistance to the ball-wedged disturbance from eccentric drive and the seat's annular area Ae exposed in the cavity as well as the seat's annular area Ac covered by the ball.
Supposing the closing seal of floating ball valves to be a non-self-energized seal, according to the concept of non-self-energized seals in Appendix 2, Division 1, Volume VIII, ASME Boiler and Pressure Vessel Code, the sealing maintaining factor m required of their seat is:
                              m          =                                                    W                s                            /                              W                u                                      ≥            2                                                        =                                                    A                s                            ⁢                              p                /                                  (                                                            A                      e                                        +                                          A                      c                                                        )                                            ⁢              p                        ≥            2                                                        =                                                    A                s                            /                              (                                                      A                    e                                    +                                      A                    c                                                  )                                      ≥            2                                    m    =                            D          s          2                                      D            o            2                    -                      D            i            2                              ≥      2      where                Ws=Asp, ball-floated sealing forces (ball-floating forces or thrust of medium on balls)        Wu=(Ae+Ac)p, unsealing forces of medium on seats (thrust of medium on seats)        As=actuating areas of medium on balls (circular areas of dia.Ds) to result in sealing        Ae=seat's annular areas exposed in cavity        Ac=seat's annular areas covered by balls, including non-contacting areas Aep         Ae+Ac=Au=annular actuating areas of medium on seats to cause unsealing        p=medium pressure, Do=outside diameters of seats        Ds=actuating diameters of balls against seats, Di=inner diameters of seats.In other words, to ensure:        Ws≧2Wu (that the ball-floated sealing force from medium is not less than twice the unsealing force of medium on the seat), or        As≧2(Ae+Ac) (that the actuating area of medium on the ball is not less than twice the annular actuating area of medium on the seat)can ensure that the seat of a floating ball valve always keeps a tight closure when impacted by disturbance, especially by ball-wedged disturbance from eccentric drive under any pressure.        
In fact, any seat of floating ball valves is an upset impulse amplifier; the ball's wedging force from eccentric drive is the input impulse, the actuation force Acp of medium on the seat's annular area covered by the ball is the output impulse, and the actuation force Aep of medium on the seat's annular area exposed in the valve body cavity is equivalent to the “D.C. output”; the greater the Aep the more beneficial to the output of impulses with a larger amplitude; actually, the greater the Aep, the more difficult the reviving of the ball clamping force W2 from the seat, and the more beneficial to that the disturbing output Acp separates the ball from the downstream seat instantaneously. The thrust Wu=(Ae+Ac)p of medium on seats is the unsealing actuation force; the greater the (Ae+Ac)p, the more enlarged the ball seating room and the more beneficial to that the ball leaves its seats for free floating but not for sealing. The thrust Ws=Asp of medium on balls is the sealing actuation force; the greater the Asp, the more beneficial to that the ball resists to its separation from its downstream seat to keep its sealing status. Therefore, m=Ws/Wu=As/(Ae+Ac) is an inherent characteristic index or the sealing maintaining factor of the ball valve seat; the greater the value of m, the better the disturbance resistance of the seat; if the disturbance resistance of the seat is not enough or the disturbance resistance index m of the seat is too small, it means that the ball-floated pressure on the downstream seat can not resist to the ball wedged disturbance from eccentric drive so as for the seat to perform its tight closure only by its clamping force W2. In fact, the ball valve whose design is like a floating ball valve but whose ball is clamped too tight by its seats to float should be called a seat-mounted ball valve or a formal or false floating ball valve. As shown in FIG. 5, the closing or working condition for formal floating ball valves is W2>Ws=Asp=m(Ae+Ac)p, and for real floating ball valves, Ws=Asp=m(Ae+Ac)p>W2.
Since the prior art has been far away from the above-mentioned sealing science and can not make use of the ball-floating force Ws from medium but can not help relying on the bigger than Ws ball-clamping force W2 from seats to realize the tight closure of floating ball valves, all the floating ball valves of the prior art must be the formal floating ball valve whose on-off ball is clamped too tight by its two seats to float within the whole working pressure range.
As to the seat of floating ball valves, since its disturbance resistance factor m=As/(Ae+Ac) (the actuating area of medium on the ball over the actuating area of medium on the seat), it is of importance to manage to reduce as fully as possible the actuating area (Ae+Ac) of medium on the seat, especially the useless exposed area Ae thereof, within the material allowable strength in order to decrease the amplified output of the ball wedged disturbance from eccentric drive and maintain a more reliable tight closure by floating ball; i.e. it is not significant to dispute if the specific value (2) of disturbance resistance factor m given above by rules of thumb is enough accurate.
According to the concepts in ASME Code, the ball preclamping force from the seats of floating ball valves as a self-energized seal is responsible only for providing the minimum seating stress y required of the seat under no medium pressure, only relevant to materials and sealing contact designs. As to a certain design of sealing contacts, the minimum seating stress y required of the seat only relates to its material yield strength, which may be construed as the stress getting the material yielded and seated into irregularities on the joint surface and whose theoretical value should approximate to the material yield strength but whose practical value is only a major percent of the material yield strength because the practical contacting area is only a major percent of the stress calculating area. According to the invention, a sealing design can always ensure its sealing material both a full microcosmic deformation stress by line contacts and a safest macrocosmic stress by surface contacts protecting the line contact from for ever disappearing, as long as the seal design is of a microline contact followed by a microsurface contact or of a microsawtoothed contact or of both a line contact followed by a surface contact and a surface contact having a permanent line contact therein. If the microline contact followed by a microsurface contact is used in the sealing design of valve seats, any valve seat, whether it is made of metal or non-metal, requires of its closing seal only a seating force so small as to be negligible because a small pressing load can produce an approximate infinite contacting stress by the microline contact whose contacting area approximates to zero. In other words, if designed by the microline contact followed by a microsurface contact and supposed to be a non-self-energized seal, a mounted seat for floating ball valves can use a ball clamping force so small as to be negligible and that a small thrust of medium on the ball can replace the ball clamping force from the upstream seat and make the ball be separated from its upstream seat, thus resulting in that the rotation resistance to the ball and the load of the seat under medium pressure is only from the thrust Ws of medium on the ball and under no medium pressure, only from the negligible ball-clamping forces W2 of the two seats.
As shown in U.S. Pat. No. 7,243,900 (CN2713240), US20030111631, U.S. Pat. No. 6,948,699, U.S. Pat. No. 4,658,847, U.S. Pat. No. 4,557,461, U.S. Pat. No. 4,502,663, U.S. Pat. No. 4,457,491, U.S. Pat. No. 4,236,691, U.S. Pat. No. 4,235,418, U.S. Pat. No. 2,963,263, U.S. Pat. No. 2,945,666 etc., the prior art has thought that the tight closure of floating ball valves is naturally self-energized but never considered the actuating area of medium on their seat, especially the influence of their seat exposure area on its self-sealing action, and neither considered the relationship between their ball-clamping force W2 and their self-energized tight closure so as to make their seat have a considerable medium actuation area (Ae+Ac) or have a high power amplifying capability for the ball wedged disturbance from eccentric drive, and hence the floating ball valves of the prior art are actually only the formal or false floating ball valve whose tight closure is realized only by the ball-clamping force W2 from the seats but not by the ball-floating force Asp from medium. Since the tight closing condition of formal floating ball valves is W2>Ws=Asp, it is necessary to ensure that their mounted seat can provide a ball clamping force W2 (>1.1Aspw) in order for them to pass the closure test of 1.1 times the working pressure pw specified by the standards, where As is the actuating area of medium on the ball. Therefore, the ultimate rotation torque of the prior floating ball valves is generated at least by the ball clamping force 2*1.1Aspw from their two seats but not by the maximum force 1.1Aspw only from one of their two seats.
In summary, it can be seen from the above analyzing of floating ball valves by applying the concept in ASME Code that supposing their closing seal to be a self-energized seal is undoubtedly not considering any influence of the other factors on the floating of their on-off ball in concepts and designs, naturally incapable of excluding the influence of the ubiquitous ball-wedged disturbance from eccentric drive so as for their closing seal to be far away from the self-sealing advantage, and unconsciously thoroughly discarding their natural ball-floating force from medium and extra using ball clamping forces from their seats for their tight closure; however, supposing their closing seal to be a non-self-energized seal comes to make their closing seal have the self-sealing advantage only to rely on their natural ball-floating force from medium but not on extra ball-clamping forces from their seats for their tight closure only by reducing the actuating area of medium on their seat or decreasing the amplifying of their ball wedged disturbance from eccentric drive; obviously, the development of knowledge about their tight closure from “self-sealing” of the prior art to “non-self-sealing” of the invention is a reversing development of thinking way and naturally results in a revolutionary change for them, which is amazing but verifiable to see that the maximum force causing their rotation resistance or the maximum load on their seats will be reduced from at least 2*1.1Aspw to at most Aspw, decreased at least by 1.1 times.
The floating ball valve is characterized by simple design, low cost and easy maintenance, while the trunnion mounted ball valve, in contrast, by complex design, high cost and difficult maintenance. The original purpose of substituting the trunnion mounted ball valve for the floating ball valve is to use another bearing instead of the downstream seat for bearing the thrust of medium on the ball in order to enable a soft seat to be burdened with a higher closing pressure, or to make a great size of ball valves not be limited to material strength of their seats. The additional result is decreasing operation torque when using the trunnion mounted ball valve instead of the floating ball valve. Since the seat of the invention can decrease the operation torque of floating ball valves of the prior art by at least 50%, the cheap and reliable floating ball valve can be substituted for the expensive trunnion mounted ball valve in a greater size if the seat of the invention can have an extra allowable compressive stress?
ISO 14313/API 6D specifies that a ball valve shall be provided with an automatic pressure relief to prevent the pressure trapped in the body cavity from exceeding 1.33 times the valve pressure rating (for the medium trapped in the body cavity when valve opens or closes will be thermally expanded to breed a dangerous pressure), and that the fire resistance design of valves shall be qualified by fire testing in accordance with ISO 10497 (API 6FA). To satisfy the requirement of the pressure relief of the ball valve cavity, U.S. Pat. No. 4,557,461, U.S. Pat. No. 4,385,747, U.S. Pat. No. 4,236,691, U.S. Pat. No. 3,488,033, GB2023773 etc. propose some complex pressure relieving seats. To pass the fire resistance test, WO82/03898 proposes a complex fire resistance design of seats. All these complex patented valve seats can be omitted if the equilateral triangle section of ball valve seats enclosed for being compressed in accordance with the invention is naturally able to satisfy the requirements of the pressure relief and the fire resistance specified in ISO 14313/API 6D?
A metallic seat of ball valves is essential for a high temperature service. However, as shown in U.S. Pat. No. 4,940,208, U.S. Pat. No. 4,502,663, U.S. Pat. No. 4,262,688, U.S. Pat. No. 4,235,418, U.S. Pat. No. 4,147,327 etc., the metallic and non-metallic seats for a floating ball valve have a design different from each other, and as shown in U.S. Pat. No. 7,032,880, U.S. Pat. No. 4,601,308, U.S. Pat. No. 4,318,420, U.S. Pat. No. 3,752,178, U.S. Pat. No. 3,164,362, U.S. Pat. No. 3,269,691 etc., the floating seat assembly for trunnion mounted ball valves has always an O-ring unsuitable for a high temperature service and results in that they have nothing to do with the metallic seat for a high temperature service. So what a wonderful thing it is supposing that the triangle-sectional seat of the invention can have the metallic and non-metallic seats for a floating ball valve unified into one design and provide a floating seat assembly without an O-ring for a mounted ball valve design!